1. Field of the Invention
The present invention relates to a differential solenoidal magnetic field sensing device having microscopic closed magnetic paths integrated on a semiconductor substrate and a manufacturing method thereof, and more particularly, to a differential solenoidal magnetic field sensing device which is integrated on a semiconductor substrate, for detecting a magnetic field weaker than a terrestrial magnetic field by forming closed magnetic paths by differentially driving two soft magnetic film cores, and a manufacturing method thereof.
2. Description of the Related Art
A magnetic sensor using a soft magnetic material and a coil has long been used as a magnetic sensor with high sensitivity. Such a magnetic sensor is manufactured by winding a coil around a relatively large rod-shaped core or an annular core made of soft magnetic ribbon. In order to accurately detect a magnetic field, an electromagnetic circuit is necessary. A method in which a magnetic field sensing element of the magnetic sensor is attained by a soft magnetic film core and a planar film coil has been proposed.
A conventional weak magnetic field sensing device is manufactured using soft magnetic film cores 1a and 1b and a planar film coil. These two cores 1a and 1b are arranged in parallel in the direction of a detection axis to then be differentially driven. This is for offsetting an induced voltage based on electromagnetic induction when no external magnetic field is applied such that an excitation coil 2a-2b and a magnetic flux variation detecting coil 3a-3b are wound around two soft magnetic film cores 1a and 1b. Thus, the conventional weak magnetic field sensing device requires a large area. Also, due to a magnetic flux variation generated by the excitation coil 2a-2b and a magnetic field detected by the magnetic flux variation detecting coil 3a-3b, leakage of magnetic flux through the soft magnetic film cores. 1a and 1b cannot be avoided, which makes it difficult to detect a magnetic field with high sensitivity.
Since the conventional weak magnetic field sensing device is manufactured by winding a coil around a relatively large rod-shaped core or an annular core made of soft magnetic ribbon, the manufacturing cost thereof is high.
To solve the above problems, it is an objective of the present invention to provide a differential solenoidal magnetic field sensing device having microscopic magnetic paths integrated on a semiconductor substrate, which can accurately detect a high-sensitivity magnetic field by minimizing the leakage of magnetic flux and can be fabricated on a microscopic scale.
It is another objective of the present invention to provide a method for manufacturing a differential solenoidal magnetic field sensing device having microscopic magnetic paths integrated on a semiconductor substrate, which cn accurately detect a high-sensitivity magnetic field by minimizing the leakage of magnetic flux and can be fabricated on a microscopic scale.
Accordingly, to achieve the first objective, there is provided a differential solenoidal magnetic field sensing device including a semiconducor substrate, soft magnetic film cores stacked on the semiconductor substrate to be laminated to form closed magnetic paths parallel to each other, a solenoidal excitation coil formed of a metal thin film for alternative excitation and differential excitation of the soft magnetic film cores, and a solenoidal magnetic flux variation detecting coil made of a metal thin film for detection of magnetic flux variation in the soft magnetic film cores.
In the present invention, preferably, the excitation coil is wound n turns where n is a positive integer, and the magnetic flux variation detecting coil is wound m turns where m is a positive integer (m being different from n), the excitation coil and the magnetic flux variation detecting coil being alternately wound turn by turn. Also, when an external magnetic field is zero, the induced waveforms caused by the excitation coil are offset.
Also, it is preferred that the excitation coil is wound around the soft magnetic film cores, in a xe2x80x9cfigure-8xe2x80x9d shape, and the magnetic flux variation detecting coil as a solenoidal planar coil is spirally wound around the soft magnetic film cores.
To achieve the second objective, there is provided a method for manufacturing a differential solenoidal magnetic field sensing device including the steps of (a) forming an insulation layer on a semiconductor substrate, (b) forming a bottom-layer wire in a coil on the insulation layer, (c) forming an insulation layer on the insulation layer of step (b) to cover the bottom-layer wire, (d) depositing a soft magnetic material for a bottom magnetic film on the insulation layer formed in step (c) and patterning the same to form a lower soft magnetic film core, (e) depositing an insulation layer to cover the lower soft magnetic film core and etching the same using photolithography to form a first throughhole, (f) forming a metal layer for a middle-layer wire on the insulation layer formed in step (e) and patterning the same to form a middle layer wire of a coil, (g) depositing an insulation layer on the insulation layer formed in step (e) to cover the middle-layer wire, depositing a soft magnetic material for a bottom magnetic film thereon and patterning the same to form an upper soft magnetic film core, (h) depositing an insulation layer to cover the upper soft magnetic film core and etching the same using Photolithography to form a second throughhole, and (i) forming a metal layer for a top-layer wire on the insulation layer formed in step (h) and patterning the same to form a top-layer wire of a coil.
In the present invention, it is preferred that the semiconductor substrate is a silicon substrate, and the bottom-layer wire, and the middle-layer wire and the top-layer wire are formed of at least one metal selected from the group consisting of aluminum (AI), gold (AU) and copper (CU). Also, when the bottom-layer wire, the middle-layer wire and the top-layer wire are formed of Al or Au, a deposition method such as a sputtering method or a CVD method is preferably used. Otherwise, when the bottom-layer wire, the middle-layer wire and the top-layer wire are formed of Cu, an electroplating method or a non-electrolytic plating method is used.
Further, the soft magnetic film cores are preferably formed of multi-layer soft magnetic films prepared by laminating a permalloy or amorphous magnetic alloy and a non-magnetic material, and the insulation layer is preferably formed of at least one of silicon oxide, photoresist or polyimide.